Use an Android tablet as a WiFi handsfree device

My situation: - Android (4.0.3) tab hooked up to my car stereo using the headphones connector. - Android (2.3.5) phone (HTC Desire HD), which I use to call, text, browse, etc. I want to make a phone call with my phone, but in my country, it is illegal to hold your phone at ear height. That is why I had a car stereo with Bluetooth, so I can hear the person I am talking to over my car speakers. Since my car stereo's Bluetooth device died, I thought I could use the Android tab as an audio relay device. The problem is: the tab has no Bluetooth. It has WiFi though. I need to replace that function and I already have a tab in my car directly connected to my stereo. I want my outgoing audio from my phone over WiFi to my tab. Phone -> WiFi -> tab -> cable -> car stereo. Is there any way to use an Android device as a hands-free adapter over WiFi? Some kind of WiFi relay between the phone and the tablet, perhaps?